Conventionally, a certain type of vehicle headlight that can illuminate an illumination area in front of the vehicle body with light by scanning the illumination area with a light spot has been known. For example, Japanese Patent Application Laid-Open No. 2009-048786 (US2009/0046474A1 corresponding thereto) discloses such a scanning type vehicle headlight, which can include a laser light source 34, a reflecting member 33 configured to reflect light from the light source 34 to an illumination area in front of a vehicle body, and an actuator 38 configured to swing (turn) the reflecting member 33 around a first axis and a second axis so that the illumination area in front of the vehicle body can be scanned with the reflected light vertically and horizontally. Herein, the vehicle headlight is illustrated in FIGS. 1 and 2 corresponding to FIGS. 12 and 13 of Japanese Patent Application Laid-Open No. 2009-048786.
In such a scanning type vehicle headlight utilizing a light spot, light beams emitted from the laser light source 34 are reflected by the reflecting member 33 while the reflecting member 33 is turned vertically and horizontally so that the reflection direction is changed, whereby generated light spots on the illumination area can be moved vertically and horizontally. Further, in order to reduce the light intensity unevenness over the illumination area, the actuator 38 can be controlled to adjust the swing speed of the reflecting member 33 around the axes depending on the swing angle of the reflecting member 33 and/or the light intensity of the light source 34 (output of the light source) can be controlled depending on the swing angle.
Note that in the vehicle headlight, the primary scanning direction in which the scanning frequency is relatively large and the secondary scanning direction in which the scanning frequency is relatively small can be set to the horizontal direction (right-to-left direction) and the vertical direction (up-to-down direction), respectively. (See the strip lines in FIG. 2B.)
In the conventional scanning type vehicle headlight illustrated in Japanese Patent Application Laid-Open No. 2009-048786, the primary scanning direction of scanning light, or the operation direction of the actuator 38 to move the reflecting member 33 at a high speed, is set to the horizontal direction in which the swing angle range of the reflecting member 33 is large. This configuration can increase the load of the actuator 38, and as a result there is the problem in which the durability of the actuator 38 may be decreased.
Furthermore, if the reflecting member 33 is turned, the turning direction of the reflecting member 33 is reversed at both ends of the swing angle range. In this case, the moving speed (swing speed) of the reflecting member 33 may be relatively faster in the center area of the swing angle range while it may be relatively slower at both ends of the swing angle range. As a result, the illumination area with the light spot may be brighter at the farthest area (cut line at the border between the bright area and the dark area) and the nearest area in front of the vehicle body in the front-to-rear direction of the vehicle while may be darker at the center area in the front-to-rear direction. The ideal illuminance distribution at the illumination area is configured such that the illuminance at areas near the vehicle body is low (dark), the illuminance at areas away from the vehicle body is changed to be high (brighter), and the maximum illuminance is near the cut line (brightest). Therefore, there has been the problem in which the illuminance distribution over the illumination area by the conventional scanning type vehicle headlight is different from the ideal illuminance distribution.
Furthermore, in order to provide such an illuminance distribution that is close to the ideal illuminance distribution, the high swing speed of such a reflecting member and/or the light intensity of the light source should be controlled depending on the swing angle and/or turning direction, resulting in complicated control for sufficient accuracy.